1. Field of the Invention
The present invention relates to semiconductor manufacturing. More particularly, the present invention relates to electrical process monitoring for semiconductor manufacturing.
2. Description of the Background Art
Automated inspection and review systems are important in process control and yield management for the semiconductor and related microelectronics industries. Such systems include optical and electron beam (e-beam) based systems.
In the manufacture of semiconductor devices, detection of physical defects and electrical failure earlier in the fabrication process is becoming increasingly important to shorten product development cycles and increase product yield and productivity. Advanced wafer inspection systems based on scanning electron microscopy technology have been used to detect defects and electrical failure as voltage contrast defects. However, as device design rules further shrink, and new processes are being widely implemented, it becomes more challenging to detect defects in device structures with smaller design rules and higher aspect ratios.
Electrical process monitoring refers to the detection of electrical characteristics and defects during manufacture of integrated circuits. Conventional techniques of electrical process monitoring include electrical probing and voltage contrast imaging.
Electrical probing disadvantageously requires special test structures to be included in the semiconductor dies being monitored. In addition, electrical probing is generally very slow and typically requires that the testing be done late in the overall process flow or at end-of-line test.
In voltage contrast electron beam imaging, the voltage of a structure being imaged determines the brightness of that structure in the image. This may be achieved by selective energy filtering to control the detection of secondary electrons in order to enhance the voltage contrast. Electron beam methods using voltage contrast may be much faster than electrical probing and may be performed in-line during the fabrication process. However, such voltage contrast techniques lack voltage-contrast sensitivity and resistance discrimination. For example, current voltage contrast methods have a voltage resolution of typically 5 to 10 volts, and a resistance resolution of about 10 megaohms. Such resolution is inadequate, except for rather crude process measurements.
What is needed is a technique for electrical process monitoring which may be performed rapidly and in-line during the fabrication process. In addition, what is needed is for the technique to have improved voltage-contrast sensitivity and hence improved resistance discrimination.